this could be a warning of your processor reaching a higher temerature than it likes most often caused by the cooling fan failing or the heatsink becoming so clogged up with dust that the fan is not able to cool the proc.
you need to open the case and power on the pc, see if the fan over the proc is spinning and if it is spinning freely. if not then a new fan will be needed.
this could happen when running a scan because of the extra cpu usage. the fact that it is happening more leads me to think it is the dust issue but check it or get it checked out before the cpu fries altogether.
of course i could be wrong but its a good place to start.